The present invention relates broadly to a microwave signal separator apparatus, and in particular to a magnetostatic wave frequency analyzer apparatus.
Magnetostatic waves, which propagate in a supporting medium such as yttrium iron garnet (YIG) films, have potential applications in microwave delay lines and filters for use in radar, electrical countermeasure equipment and communication systems. Constant delay lines with bandwidths of 400 megahertz and delays of about 100 nanoseconds and linear dispersive chirp delay lines with bandwidths of about 1 gigahertz and differential delays of 200 nanaoseconds have been demonstrated at 9 gigahertz.
A forward surface wave is generated by the input transducer if a magnetic biasing H field is applied in the plane of the film but perpendicular to the direction of propagation. A forward volume wave is generated by the input transducer if the H field is normal to the plane of the film. A backward volume wave is formed by an input transducer when the magnetic biasing H field is in the plane of the film in the direction of propagation of the magnetostatic wave. Typically a magnetostatic wave is generated by passing current through a wire or conductor which is placed adjacent to the YIG film. The magnetic field that surrounds the wire induces the magnetostatic wave which propagates in the YIG film in a direction that is dependent upon the magnitude and orientation of an external magnetic field that created the magnetic biasing H field in the film.
A YIG film of finite width is effectively a magnetostatic waveguide and, in common with electromagnetic and acoustic waveguides, can support the usual desired lowest order mode plus higher order modes of magnetostatic waves. With magnetostatic surface waves, only higher order width modes can exist but with magnetostatic volume waves both higher order thickness and width modes can exist. Higher order modes are launched, along with the lowest order mode, by the input transducer with a launching efficiency that is dependent upon the transducer geometry. Higher order modes of magnetostatic waves are also produced by scattering of the lowest order mode by defects in the YIG film. At the receiving transducer the highest order modes interfere with the lowest order mode, producing amplitude and phase ripple as well as increasing the overall insertion loss of the delay lines.